Present day society has grown accustomed to living in a thermally controlled environment, that is, an environment which is "conditioned" by being either heated or cooled to a comfortable level. Not only is the temperature, humidity, etc. of the air controlled, but also, present day society demands the instantaneous provision of "on-tap" hot and cold water, swimming pools heated to a comfortable level, etc. For example, in the domestic situation, it is not uncommon for persons to demand an air conditioned home with a heated pool, etc. Holiday resorts have even more demanding requirements, such as air conditioned rooms, heated swimming pools, refrigerated rooms for containment of foodstuffs, high temperature rooms such as saunas, etc.
Obviously, all these individual components of a domestic, business or resort premises have high demands for energy, which result in high fuel prices. With the increased cost of fuel, and electricity in recent times, such systems have consequently become more and more expensive to operate.
Not only do persons demand such controlled environments, but, they demand different comfort levels in different seasons. That is, the demands of winter and summer, for example, are different.